The present invention relates to an apparatus and process for the synchronization of a plurality of square, subdivided signals wherein the signals are of the type produced by subdividing an analog periodic scanning signal generated by a scanning unit during the scanning of a measuring graduation.
It is well known in incremental length or angle measuring systems that periodic analog signals are generated by a scanning unit in the process of scanning a grid-type incremental measuring graduation. To determine the direction of movement and to avoid the occurrence of symmetry errors in the scanning signals, the scanning operation is often performed with four scanning fields wherein each field is offset to one another in the measuring direction by a quarter of the grid graduation period.
For many measurement applications, the resolution corresponding to the grid graduation is not sufficient. A large number of proposals have been made to subdivide the scanning signals and to thereby increase the resolution of the measurement.
In Swiss Pat. No. 407,569, a subdivision circuit is disclosed wherein a plurality of trigger circuits are used to subdivide and thereby increase the number of the scanning signals. However, the circuit described in this publication offers no assurance that, with increasingly finer subdivisions, the trigger signals are precisely synchronized with respect to their sequence and edge spacing. Without precise synchronization, inaccurate counting in the incremental evaluation of the square signals may occur. The inaccuracy of the count may be dependent upon the degree of subdivision, the measuring speed, and interfering influences of an electrical and mechanical nature, including interference pulses, jarrings, and the like.
In addition, excessively small edge spacings, overlappings or inadmissible signal states or sequences of the trigger signals may occur with increasingly finer subdivisions. All of these conditions may lead to a reduction in measuring accuracy.
During relative movement of the measuring instrument and the measured object, the inaccuracy of the countings may not be perceptible. The imperceptibility may arise because the least significant digits of the evaluating unit display are undergoing such a rapid change in their displayed values that they are unreadable. However, when relative movement of the measuring system and the measured object ceases, the entire display value is readable. It is then important that the measuring system provide assurance that all the graduation increments and all the square signals produced by subdivision have in fact been counted. The sum, or, in the case of a negative measuring direction, the difference, of all the increments traversed must correspond exactly to the display value. It is this value that represents the measure of the path traversed.
If the square signals that have been obtained from the scanning signals by subdivision have such a small edge spacing that an accurate counting is not possible, then all of the square signals may not be counted. An inaccurate counting results in a measurement value being displayed in the evaluating unit which is lower than the value which actually represents the travel of the measuring apparatus.
The other conditions cited above which produce faulty measuring signals may also lead to similar inaccurate measurement results.
It is an object of the present invention to provide an apparatus and process for synchronizing the triggered square signals to the excessively small edge spacings of the successive subdivided, square signals and for correcting faulty transition states of the square signals.